The same rehabilitation program was used for each patient. After the acute phase, the patients were permitted to exercise to promote increased range of motion. They used isotonic knee extension and flexion exercises. The patients were allowed partial weight bearing at 2 postoperative weeks and progressed to full weight bearing at postoperative week 3. Rehabilitation exercises involved stationary bicycling and exercises with partial weight bearing at 3 weeks after surgery. Isotonic strengthening exercises for the quadriceps and hamstring muscle were initiated at week 4. Until week 8, a restriction in the range of motion was set for the knee extension exercise. Jogging and full-speed running were permitted after 12 and 16 postoperative weeks, and progressed to agility and sports-specific drills. Return to unlimited sports activity was allowed at 6–8 postoperative months.

Subjects answered the questions of a standard questionnaire to provide a Knee Injury and Osteoarthritis Outcome Score (KOOS). The questionnaire’s answers provide an internationally used orthopaedic patient self-assessed outcome score. The KOOS supplies a global assesment (symptoms/stiffness, pain, functional impact on every day activities and sports activities, and quality of life) of post-traumatic or degenerative knee conditions. Each subscale score of 36 questions is calculated independently. The mean score of the individual items of each subscale are calculated and divided by 4. Scores for the summed (overall KOOS) and individual subdomains are transformed to a scale of 0–100, with 0 representing extreme knee problems and 100 representing no knee problems. For a detailed explanation, consult Roos et al. (1998).

We evaluated 4 single-leg function tests: (1) single hop for distance; (2) 6-m timed hop; (3) triple hop for distance; and (4) cross-over hop for distance (Fig. 20.1) (Noyes et al. 1991). For each hop test, the subjects performed one practice trial for each limb, followed by two measured and recorded trials. The final landing on the hop limb had to be stabilized and held for 2 s to be recorded as a successful trial. Subjects were instructed to begin with the nonoperative leg, with their lead toe behind a marked starting line. For single hop for distance, the subjects stood on the leg to be tested. The athlete was instructed to initiate the hop by swinging the arms forward, simultaneously extending at the hip and knee, and to hop forward as far as possible while being able to land safely on the same limb. In the triple hop for distance, the subjects stood on one leg and performed three consecutive hops going as far as possible, using the same limb. In the crossover hop for distance, the subjects were instructed to land safely on the same foot, but on the opposite side of the line medial to the stance limb. Athletes were instructed to immediately redirect into two subsequent forward directed hops, crossing over the midline with each hop. For the 6-m timed hop, the subjects stood on one leg, and then hopped as fast as possible over a marked distance of 6 m. The fastest time measured using the Speed Trap timing system (Brower Timing Systems, Utah, USA) was used for data analysis. The hop test scores were calculated as the average of two recorded trials for each limb. We used the hop test scores of the four tasks to calculate a limb symmetry index (LSI) as per the following formula: (operated lower extremity/nonoperated lower extremity) × 100 %.

Isokinetic concentric strength was measured in the both limbs using a dynamometer (Biodex System III, Biodex Co., New York, USA) (Fig. 20.2). Before evaluation, compensation was performed to exclude the effect of gravity on the measurement of torque. The subject was first supervised in the performance of the movements, and then allowed several practice trials. Three trials of isokinetic contraction were performed at angular velocities of 60° and 180°/s. The range of motion was set from 90° of knee flexion to full extention. The reconstructed limb was tested before the uninjured limb. During the isokinetic contraction, the values for the peak torque were recorded for analysis and normalized to body weight. We calculated LSI by using the same formula as with the hop testing.

Means and standard deviations were calculated for all variables of interest. All statistical analyses were conducted using a statistical analysis software program (SPSS ver. 21.0; SPSS Japan, Tokyo, Japan). A paired t-test was used to test for side-to-side differences in each hop test and for isokinetic strength. To compare differences between males and females, a non-paired t-test was performed on the hop tests and strength LSI evaluations. A Pearson’s product–moment correlation coefficient (r) was used to examine the relationship among hop test LSI, strength LSI and overall KOOS scores. Statistical significance was established at p <0.05.